1. Field of the Invention
The present invention relates to a radio terminal device (which is also referred to as a wireless terminal device) having a plurality of communication interfaces and a radio communication system (which is also referred to as a wireless communication system) including such radio terminal devices.
2. Description of the Background Art
In recent years, the realization of home network is attracting much attention, and in particular, the IEEE 1394 for connecting between digital home electronic devices has been attracting considerable attention. The IEEE 1394 bus is capable of connecting a plurality of terminals in daisy chain or star connection and transferring a wideband data in excess of 100 Mbps. Also, it has a major feature that it is possible to transmit both asynchronous data and isochronous data on the same cable. For this reason, even though the IEEE 1394 bus was originally developed as a next generation version of SCSI, there are increasing trends to use the IEEE 1394 bus as a cable for connecting AV devices.
On the other hand, the realization of fast radio network (radio LAN) is also attracting attention. In particular, since the determination of the IEEE 802.11 specification in 1998, many radio LAN products are appearing in the market and there has been a remarkable decrease in the prices of these radio LAN products.
In conjunction with this trend for improved performance and reduced cost of the radio technology, there is an active trend to consider applications of the radio technology to the home environment and this trend is expected to grow further in future as can be anticipated by establishment of organizations such as HomeRF and Bluetooth in the U.S.A. Also, from a viewpoint of the home network, the radio system is an easily acceptable system as it does not require any new cable construction. For this reason, the fast radio LAN system is expected to play a central role in the future home network.
However, there are some outstanding problems in the application of a radio network to the home environment. One such problem is the realization of a wideband data transfer using radio. Data to be transferred in the home are expected to be mostly video data such as those of TV broadcast or satellite broadcast, so that the realization of a radio system capable of transferring such wideband data is crucial for wider spread of radio systems in the home environment.
To this end, a radio system using 5 GHz band is currently proposed. This proposition is aimed at the realization of a radio system capable of realizing the transmission rate of about 20 to 30 Mbps, by which several channels of MPEG2 video data can be transferred. Also, the 5 GHz band radio frequencies are said to be the last frequencies that can penetrate through many walls present in the home environment, so that this is the most promising candidate for the wideband radio system for home use.
But the 5 GHz band radio system also has its own problems. Namely, it is currently impossible to realize LSI of the RF function using CMOS. This is a severe drawback in view of a low cost realization of the 5 GHz radio system, and its resolution is imperative since it is expected that wider spread of radio systems in the home environment critically depends on how cheaply this 5 GHz band radio system can be offered to the general users.
As described, a radio device for transferring wideband data such as 5 GHz band radio system is expected to be rather expensive, and for this reason it is expected that a cost of the radio terminal itself will be very high in realizing the video data delivery in the home environment. This is a very serious problem for very cost sensitive products such as home electronic devices.